(655c) Characteristics of Reactive Composite Boron/Iron Oxide/Polytetrafluoroethylene Materials

Characteristics of reactive composite boron/iron oxide/polytetrafluoroethylene materials

Song Wang¹, Edward L. Dreizin¹, Demitrios Stamatis², Gregory Young²

¹ New Jersey Institute of Technology, Newark, NJ 07102

² Naval Surface Warfare Center EOD Tech Div, Indian Head, MD 20640

Abstract

Boron as a fuel is attractive thermodynamically; however, its performance in practical energetic formulations is often inadequate.  One of the substantial drawbacks of using boron in propellants is generation of condensed reaction products, leading to reduction in the specific impulse.  Boron ignition delays caused primarily by its surface oxide film constitute another significant obstacle to its use in various energetic formulations.   Combusting boron in fluorinated formulations is expected to generate gas-phase BOF, reducing the effect of condensed oxides.  Adding reaction modifiers, especially those promoting heterogeneous oxidation of boron, is expected to shorten boron ignition delays.  In this work, ternary compositions combining boron with polytetrafluoroethylene (PTFE) and iron (III) oxide are prepared and characterized.

Materials are prepared by ball-milling starting components; reference samples are prepared, for which ball milling is replaced by powder blending.   A shaker mill is used for all prepared ball-milled samples.  The milling includes two steps: a binary composite is prepared in the first step and the third component is added during the second step.  The order in which components are added is changed systematically.  Materials with different specific compositions are prepared and characterized.  Prepared binary and ternary samples are characterized using electron microscopy and x-ray diffraction.  Their reactivity is characterized using thermo-analytical measurements.  Finally, ignition of the prepared materials is characterized using an electrically heated filament.  The heating rates varied in the range of 2500-13000 K/s.

Two types of PTFE with different densities are examined. It is observed that the morphology of PTFE is affected substantially by milling process, and large PTFE fibers are formed and detected in the SEM images after milling.  In addition, milling PTFE and Fe₂O₃, caused substantial changes in both melting and decomposition temperatures of PTFE.  Milling PTFE does not appear advantageous and its blending with the milled B-Fe₂O₃ powders is proposed as a more streamlined practical material preparation process.  The type of PTFE does not noticeably affect reactivity of the prepared composites.  Significant exothermic peaks, leading to ignition are detected and are found to be primarily affected by the B-Fe₂O₃ thermite reactions, similar for both binary B-Fe₂O₃ and ternary compositions.  Adding Fe₂O₃ to boron reduces its ignition temperature.  Binary B-PTFE material ignites above 1173 K.  The lowest ignition temperature recorded for the ternary material prepared by milling B and Fe₂O₃ and subsequent blending with PTFE is 793 K. The temperature is lower for the ball-milled materials as compared to materials with the same bulk compositions prepared by blending powders.